# What this PR does
This PR:
- adds a new method
`apps.schedules.ical_utils.get_cached_oncall_users_for_multiple_schedules`.
In short this method basically adds a layer of caching on top of
`apps.schedules.ical_utils.get_oncall_users_for_multiple_schedules`. We
store one cache value for each schedule. Cache results are stored for 15
minutes. To me this feels like a good balance between improving
performance + returning stale results. Cache values are stored as:
- key = `f"schedule_{schedule.public_primary_key}_oncall_users"`
- value = `[user.public_primary_key for user in
schedule.currently_oncall_users]`
- adds a `DELETE /alertgroups/<id>` internal API endpoint (needed by
Grafana Incident for the Add Responders integration)
- updates the `is_currently_oncall` query parameter for the `GET /users`
internal API endpoint to return ALL users when the query param value `==
"all"`
## Which issue(s) this PR fixes
https://github.com/grafana/oncall-private/issues/2264
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)
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